[RFC PATCH 6.6.y 4/4] misc: ti-st: synchronize TTY teardown with transport removal

[Hongyan Xu <getshell@seu.edu.cn>]

Unregistering the line discipline does not close an instance which is
already attached to a TTY.  Its callbacks and work_write_wakeup can keep
using the transport after st_core_exit() frees it.

Protect the attached TTY pointer with the core lock.  On removal, take a
TTY reference and synchronously hang it up, then cancel the wakeup work
before releasing the core.  Also cancel the work in normal close and clear
disc_data only after the close cleanup is complete.

Fixes: 53618cc1e51e ("Staging: sources for ST core")
Cc: stable@vger.kernel.org
Signed-off-by: Hongyan Xu <getshell@seu.edu.cn>
---
 drivers/misc/ti-st/st_core.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/misc/ti-st/st_core.c b/drivers/misc/ti-st/st_core.c
index 3aed6c3..7610656 100644
--- a/drivers/misc/ti-st/st_core.c
+++ b/drivers/misc/ti-st/st_core.c
@@ -723,13 +723,18 @@ EXPORT_SYMBOL_GPL(st_unregister);
 static int st_tty_open(struct tty_struct *tty)
 {
 	struct st_data_s *st_gdata __free(st_kim) = NULL;
+	unsigned long flags;
+
 	pr_info("%s ", __func__);
 
 	st_kim_ref(&st_gdata, 0);
 	if (!st_gdata)
 		return -ENODEV;
+
+	spin_lock_irqsave(&st_gdata->lock, flags);
 	st_gdata->tty = tty;
 	tty->disc_data = st_gdata;
+	spin_unlock_irqrestore(&st_gdata->lock, flags);
 
 	/* don't do an wakeup for now */
 	clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
@@ -757,6 +762,7 @@ static void st_tty_close(struct tty_struct *tty)
 	struct	st_data_s *st_gdata = tty->disc_data;
 
 	pr_info("%s ", __func__);
+	cancel_work_sync(&st_gdata->work_write_wakeup);
 
 	/*
 	 * TODO:
@@ -777,7 +783,6 @@ static void st_tty_close(struct tty_struct *tty)
 	 * N_TI_WL ldisc is un-installed
 	 */
 	st_kim_complete(st_gdata->kim_data);
-	st_gdata->tty = NULL;
 	/* Flush any pending characters in the driver and discipline. */
 	tty_ldisc_flush(tty);
 	tty_driver_flush_buffer(tty);
@@ -791,6 +796,8 @@ static void st_tty_close(struct tty_struct *tty)
 	st_gdata->rx_state = ST_W4_PACKET_TYPE;
 	kfree_skb(st_gdata->rx_skb);
 	st_gdata->rx_skb = NULL;
+	st_gdata->tty = NULL;
+	tty->disc_data = NULL;
 	spin_unlock_irqrestore(&st_gdata->lock, flags);
 
 	pr_debug("%s: done ", __func__);
@@ -905,6 +912,8 @@ err_unreg_ldisc:
 
 void st_core_exit(struct st_data_s *st_gdata)
 {
+	struct tty_struct *tty;
+	unsigned long flags;
 	long err;
 
 	if (!st_gdata)
@@ -914,6 +923,14 @@ void st_core_exit(struct st_data_s *st_gdata)
 	wait_event(st_gdata->users_wait,
 		   !atomic_read(&st_gdata->active_users));
 
+	spin_lock_irqsave(&st_gdata->lock, flags);
+	tty = tty_kref_get(st_gdata->tty);
+	spin_unlock_irqrestore(&st_gdata->lock, flags);
+	if (tty)
+		tty_vhangup(tty);
+	cancel_work_sync(&st_gdata->work_write_wakeup);
+	tty_kref_put(tty);
+
 	/* internal module cleanup */
 	err = st_ll_deinit(st_gdata);
 	if (err)
-- 
2.50.1.windows.1